This invention relates in general to vehicles, and, more particularly, to trucks having a dump bed which can be elevated at a forward end to dump material which is loaded on the bed.
A variety of trucks utilize a dump bed which is pivotally mounted at the trailing end and is connected to an extensible cylinder at a forward end. Extension .of the cylinder raises the forward end of the dump bed to cause the material carried on the bed to slide rearwardly off of the bed. When the dump bed is to be returned to its normal horizontal position, the cylinder actuating force is simply released and the weight of the dump bed causes retraction of the cylinder and lowering of the bed.
While the dump beds of the type described are suitable for dumping loads of free-flowing particulate material such as sand and gravel, other materials such as mud and asphalt can be difficult to remove because they have a tendency to stick together in a single mass and adhere to the bed surface. Removal of such materials often requires the truck operator to move the vehicle forwardly in a lurching motion which separates the material from the bed but also subjects the various components of the dumping mechanism to large stresses which can cause twisting and eventual fracturing of one or more components.
Certain types of dump beds are designed so that the bed can be elevated to an angle greater than 45 degrees to facilitate removal of material from the bed. Because the cylinder which causes elevation of the bed is normally connected to the forward end of the bed, the cylinder must have an exceedingly long stroke in order to move the bed through an angle of 45 degrees or more. Although multi-stage cylinders can be used to provide the desired stroke, they tend to be much more expensive than single-stage, single acting cylinders.
In addition to the increased costs associated with the types of cylinders required to move the bed through a large angle of movement, such dump beds tend to be very unstable when the bed is fully raised because the pivot axis is usually located immediately below the undersurface of the bed. This location of the pivot axis creates a large moment arm when the bed is fully raised and if the load being carried should be imbalanced or if it should suddenly shift, the bed may sway violently from side to side and damage the suspension or dumping components. In some instances, the swaying may be severe enough to place the vehicle at risk of tipping over sideways.
When small utility trucks are equipped with dump beds, they can be used to transport and unload a variety of bulk items ranging from large hay bales to tractor wheels to vehicle engines. Such dumps beds, however, are usually not self-loading. As a result, items which because of their size or bulk cannot be hand loaded onto the bed require the assistance of a forklift, tractor or similar mechanism. Often, however, such assistance is unavailable or inconvenient and the usefulness of the vehicle is limited accordingly. A need has thus developed for a dump bed which is more stable and less expensive than those currently available and which can be more easily loaded. These features would be particularly desirable in a dump bed which could be used with small utility vehicles such as pickup trucks.